Finely divided metal oxides and sintered objects therefrom

Abstract

Finely-divided metal oxides are prepared by the steps of (a) contacting a compound of a metal with a carbohydrate material to obtain an intimate mixture thereof, (b) igniting this mixture to oxidize the same and to insure conversion of substantially all of said metal compound to a fragile agglomerate of its metal oxide, and (c) pulverizing the product of step (b) to form a finely-divided metal oxide powder having a mean particle size below about 1.0 micron. Certain of the finely-divided metal oxide powders produced by this process have the useful property of sinterability at temperatures significantly lower than metal oxide powders heretofore readily available. The powders are useful in the preparation of high strength compacted shapes for use in high temperature and/or corrosive environment, in the preparation of refractory cements, catalysts, catalysts supports and the like.

What is claimed is: 
     
       1. Process for producing finely divided metal oxygen-containing compounds which comprises: a. contacting a carbohydrate material with at least one compound of a metal to form an intimate mixture thereof;   b. introducing said mixture into a heating zone having a temperature sufficient to ignite said mixture but insufficient to substantially sinter said metal compound;   c. igniting said mixture in said heating zone for a time period sufficient to decompose and remove said carbohydrate material and produce easily disrupted agglomerates of submicron size metal oxygen-containing particles;   d. disrupting said agglomerates without substantially reducing the size of the individual particles which comprised said agglomerates to produce finely divided metal oxygen-containing compounds having a mean particle size below one micron.   
     
     
       2. The process of claim 1 wherein said carbohydrate material is cellulosic. 
     
     
       3. The process of claim 1 wherein said carbohydrate material is wood pulp. 
     
     
       4. The process of claim 1 wherein said carbohydrate material is cotton. 
     
     
       5. The process of claim 1 wherein said carbohydrate material is a sugar. 
     
     
       6. The process of claim 5 wherein said sugar is sucrose. 
     
     
       7. The process of claim 5 wherein said sugar is invert syrup. 
     
     
       8. The process of claim 1 wherein said metal oxygen-containing compound is a metal oxide. 
     
     
       9. The process of claim 1 wherein said metal oxygen-containing compound is a ferrite. 
     
     
       10. The process of claim 1 wherein said oxygen-containing compounds are comprised of at least one metal which is selected from the group consisting of beryllium, magnesium, calcium, the Group III B metals, the Group IV B metals, niobium, tantalum, the Group VI B metals, manganese, iron, cobalt, nickel, copper, zinc, cadmium, aluminum; gallium, tin, lead and bismuth. 
     
     
       11. The process of claim 1 wherein said oxygen-containing compounds are comprised of at least one metal which is selected from the group consisting of beryllium, magnesium, calcium, the Group IIIB metals, the Group IVB metals, niobium, tantalum, the Group VIB metals, manganese, iron, cobalt, nickel, copper, zinc, cadmium, aluminum, gallium, tin, lead and bismuth, and at least one additional metal selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, strontium, barium, germanium, vanadium, ruthenium, osmium, rhodium, indium, iridium, thallium and antimony. 
     
     
       12. Process of claim 1 wherein in step (a), said metal compound comprises an aqueous solution of a zirconium compound. 
     
     
       13. Process of claim 12 wherein said aqueous solution of a zirconium compound also contains dissolved therein a compound of a metal that forms an oxide that stabilizes zirconia. 
     
     
       14. Process of claim 13 wherein said metal that forms an oxide that stabilizes zirconia is yttrium. 
     
     
       15. Process of claim 12 wherein the zirconia is comminuted by wet ball milling. 
     
     
       16. Process of claim 12 wherein said aqueous solution of a zirconium compound also contains dissolved therein at least one copper and at least one chromium compound that forms an oxide. 
     
     
       17. Process of claim 1 wherein in step (a), said metal compounds comprise at least one barium and one titanium compound, said mixture being essentially free of chloride ions. 
     
     
       18. A process for the preparation of submicron barium titanate powders which process comprises the steps of: a. contacting a water soluble carbohydrate with an aqueous acidic solution of a tetraalkyl titanate and an aqueous solution of barium alkanoate, to form an intimate mixture thereof, said mixture being essentially free of chloride ions,   b. introducing said mixture into a heating zone having a temperature sufficient to ignite said mixture but insufficient to substantially sinter said barium titanate compound;   c. igniting said mixture in said heating zone for a time period sufficient to decompose and remove said carbohydrate material and produce easily disrupted agglomerates of sub-micron size barium titanate particles,   d. disrupting said agglomerates without substantially reducing the size of the individual particles which comprised said agglomerates to produce finely divided barium titanate powder having a mean particle size below one micron.   
     
     
       19. The process of claim 17 wherein said barium and titanium compounds are organic compounds. 
     
     
       20. The process of claim 17 wherein said barium compound is barium acetate. 
     
     
       21. The process of claim 17 wherein said titanium compound is triethanolamine titanate. 
     
     
       22. The process of claim 17 wherein said titanium compound is tetraisopropyl titanate. 
     
     
       23. The process of claim 17 wherein said barium titanate also contains other metal oxides. 
     
     
       24. A process for producing a sintered article comprised of a metal oxide which is sinterable to essentially its theoretical density at low temperatures, sid article having a compressive strength of at least 5,000 pounds per square inch, which process comprises: a. contacting a carbohydrate material with a compound of a metal to form an intimate mixture thereof;   b. introducing said mixture into a heating zone having a temperature sufficient to ignite said mixture but insufficient to substantially sinter said metal compound;   c. igniting said mixture in said heating zone for a time period sufficient to decompose and remove said carbohydrate material and produce easily disrupted agglomerates of metal oxide particles of sub-micron size,   d. disrupting sid agglomerates without substantially reducing the size of the individual particles which comprised said agglomerates to produce finely divided metal oxide powder having a mean particle size of less than 0.1 micron,   e. shaping and compacting said powder into the form of said article, and   f. sintering said shaped article at a temperature and for a period of time sufficient to form said article.   
     
     
       25. A process for producing a sintered article comprised of zirconia essentially at its theoretical density, said article having a compressive strength of at least 5,000 pounds per square inch, which process comprises: a. contacting a carbohydrate material with a compound of zirconium to form an intimate mixture thereof;   b. introducing said mixture into a heating zone having a temperature sufficient to ignite said mixture but insufficient to substantially sinter said zirconium compound;   c. igniting said mixture in said heating zone for a time period sufficient to decompose and remove said carbohydrate material and produce easily disrupted agglomerates of zirconia particles of sub-micron size,   d. disrupting said agglomerates without substantially reducing the size of the individual particles which comprised the agglomerates to produce finely divided zirconia powder having a mean particle size of less than 0.1 micron,   e. shaping and compacting said powder into the form of said article, and   f. sintering said shaped article, at a temperature and for a period of time sufficient to form said article.   
     
     
       26. A process for producing a sintered article comprised of thoria essentially at its theoretical density, said article having a compressive strength of at least 5,000 pounds per square inch, which process comprises: a. contacting a carbohydrate material with a compound of thorium to form an intimate mixture thereof;   b. introducing said mixture into a heating zone having a temperature sufficient to ignite said mixture but sufficient to substantially sinter said thorium compound;   c. igniting said mixture in said heating zone for a time period sufficient to decompose and remove said carbohydrate material and produce easily disrupted agglomerates of thoria particles of sub-micron size,   d. disrupting said agglomerates without substantially reducing the size of the individual particles which comprised the agglomerates to produce finely divided thoria powder having a mean particle size of less than 0.1 micron,   e. shaping and compacting said powder into the form of said article, and   f. sintering said shaped article, at a temperature and for a period of time sufficient to form said article.   
     
     
       27. The sintered article comprised of thoria prepared by the process of claim 26. 
     
     
       28. A process for producing a sintered article comprised of erbia essentially at its theoretical density, said article having a compressive strength of at least 5,000 pounds per square inch, which process comprises: a. contacting a carbohydrate material with a compound of erbium to form an intimate mixture thereof;   b. introducing said mixture into a heating zone having a temperature sufficient to ignite said mixture but insufficient to substantially sinter said erbium compound;   c. igniting said mixture in said heating zone for a time period sufficient to decompose and remove said carbohydrate material to produce easily disrupted agglomerates of erbia particles of sub-micron size,   d. disrupting said agglomerates without substantially reducing the size of the individual particles which comprised the agglomerates to produce finely divided erbia powder having a mean particle size of less than 0.1 micron,   e. shaping and compacting said powder into the form of said article, and   f. sintering said shaped article, at a temperature and for a period of time sufficient to form said article.   
     
     
       29. A sintered article comprised of erbia prepared by the process of claim 28. 
     
     
       30. A process for producing a sintered article comprised of two or more metal oxides, said article having a surface area which is at least 10 square meters per gram, and a compressive strength of at least 5,000 pounds per square inch, which process comprises: a. contacting a carbohydrate material with two or more compounds of a metal to form an intimate mixture thereof;   b. introducing said mixture into a heating zone having a temperature sufficient to ignite said mixture but insufficient to substantially sinter said metal compounds;   c. igniting said mixture in said heating zone for a time period sufficient to decompose and remove said carbohydrate material and produce easily disrupted agglomerates of metal oxide particles of sub-micron size, at least some of which metal oxide particles are sinterable;   d. disrupting said agglomerates without substantially reducing the size of the individual particles which comprised said agglomerates to produce finely divided metal oxide powder having a mean particle size of less than 0.1 micron,   e. shaping and compacting said powder into the form of said article, and   f. sintering said shaped article, at a temperature and for a period of time sufficient to form said article.   
     
     
       31. The process of claim 30 wherein said sintered article is comprised of the oxides of zirconium and aluminum. 
     
     
       32. The process of claim 31 wherein said oxide of aluminum is present in an amount of from about 5 to about 70 weight percent. 
     
     
       33. The process of claim 30 wherein said sintered article is comprised of the oxides of copper and aluminum. 
     
     
       34. The process of claim 33 wherein said oxide of aluminum is present in an amount of from about 5 to about 70 weight percent. 
     
     
       35. A sintered article comprised of the oxides of copper and aluminum, said article being prepared by the process of claim 30. 
     
     
       36. The sintered article of claim 35 wherein aid oxide of aluminum is present in an amount of from about 5 to about 70 weight percent.